1. Field of the Invention
The invention relates to a method and a device for monitoring temperature distributions and/or temperature anomalies on the basis of distributed fiber-optic temperature sensing as well as to novel applications of such methods.
2. Description of the Related Art
Distributed fiber-optic measurement principles use the integration of laser light impulses into an optical waveguide and the scattering effects thereof. The scattering of the laser light impulse takes place on the molecules of the optical waveguide. A small part of the laser light is thereby scattered back. The intensity and the spectral composition of the scattered light is accordingly determined by the molecules in the optical waveguide and by the behavior of the molecules.
The backscattered light is composed of different spectral portions, which are caused by different mechanisms of the interaction between laser light and the optical waveguide components and which thereby also include different information on the physical state of the optical waveguide. Thus, however, the optical waveguide itself turns into a sensitive element.
The Rayleigh backscatter component, which has the same wavelength as the integrated primary laser impulse, provides the highest peak in the scattered light spectrum and thereby essentially determines the exponential drop of the intensity time curve of the backscattered light. As inhomogeneities in the optical waveguide, local attenuation changes, micro ruptures, splice connections and the like cause the intensity in the Rayleigh backscatter component to change, said component of the scattered light spectrum is used for controlling the quality of optical waveguides or for error detection, respectively.
The interaction of the laser light with optical phonons in the optical waveguide, i.e. the scattering of the phonons on thermal grid vibrations in the material, is the cause for the Raman backscatter components.
The Raman scattered light consists of two components, the so-called stokes line and the anti-stokes line. Said two spectral lines lie symmetrically to the peak of the Rayleigh backscatter, shifted by a certain amount of the wave number. While the intensity of the stokes line IS shifted to smaller wave numbers is virtually temperature-independent, the anti-stokes line IA shifted to higher wave numbers is clearly dependent on the temperature, whereby the utilization of the Raman backscatter is pre-destined for the distributed temperature measurement.
The sole consideration of the information contained in the backscatter spectrum of an optical waveguide does not yet provide any information on the local distribution along the optical waveguide. The so-called OTDR method is used for backscatter measurements for the locally resolved detection of the attenuation by means of the Rayleigh scattering. In order to be able to realize a distributed, i.e. locally resolved detection of the temperature by means of the Raman sensing mechanism, either the aforementioned OTDR method (Optical Time Domain Reflectometry) is used as time domain reflectometry measurement or the OFTR (Optical Frequency Domain Reflectometry) is used as frequency domain reflectometry measurement.
The OTDR method is based on a pulse/echo principle, i.e. the intensity (scatter level) and the place of origin (scatter location) of the backscattered Raman light are determined on the basis of the time interval between sending and detecting the light impulses.
The alternative OFTR technology enables a quasi permanent operation of the laser and a narrow-band detection of the optical backscatter behavior. The so obtained advantages enable the use of more inexpensive laser light sources and cost-saving electronic components for the signal detection. In contrast thereto, however, the more problematical measurement of the scattered light and a signal processing with higher linearity requirements, which is more laborious due to the Fourier transformation, have to be taken into account.
The German laid-open print DE 195 09 129 A1 discloses a method and a device for controlling and monitoring the state of pipes, containers, pipelines and the like.
According to said teaching it is assumed that the liquid or gaseous media contained in said pipes, containers or pipelines have a different media temperature relative to the direct ambience. The ambient temperature distribution is determined at least above sections along and/or peripheral of and/or in the bottom region close to the pipes, containers, pipelines or the like, however, externally of the media space enclosed thereby.
Said temperature determination is performed with an elongated distributed temperature sensor in the form of a fiber-optic sensor cable for detecting the temperature on the basis of the aforementioned principles. If a local anomaly in the temperature distribution is detected, a leakage is assumed and the location, the direction of spreading and the leakage quantity are then determined from the temperature distribution at the respective location of the anomaly or the changing location of the anomaly.
In respect of the device according to DE 198 09 129 A1 the elongated temperature sensor, i.e. the fiber-optic sensor cable is arranged directly at or adjacent over a predetermined clearance within a pipe trench or a pipe bridge longitudinally of the pipe at the circumference of the outer surface of said pipe.
With substantially horizontally extending pipes, pipelines or the like the elongated sensor is fixed underneath the pipes. In this respect it is useful to also fix a plurality of temperature sensors or cables, which extend essentially parallel, parallel to the longitudinal axis underneath thereof so that the spreading direction and the spreading quantity of a media discharge caused by a leakage can be determined. At particularly endangered spots the aforementioned solution suggests to provide several or more densely arranged temperature sensors in order to also identify smallest leakages with a high location-related measurement accuracy.
The basis for leakage detection is the knowledge that a penetrating medium having a higher or lower temperature in relation to the ambient temperature results in a local temperature change, which also includes the direct ambience of the pipe or container jacket.
The advantageously used fiber-optic sensor cables known per se can evaluate the time interval and intensity of backscattered light with cable lengths of up to 10 km, arriving at a temperature resolution of 0.1xc2x0 C. The given resolution of the location lies within 1 and 0.25 m in response to the length of the sensor cable and the selected method.
The German utility model G 93 18 404 discloses a device for determining temperatures on or in extended measurement objects, wherein the system shown therein uses an optic-electronic measurement device. Said known measurement device feeds a laser impulse on at least one end of an optical waveguide and serves to examine the radiation backscattered by the optical waveguide. Due to the already explained interactions the temperature and the location can then be evaluated longitudinally of the optical waveguide in dependence on the spectrum and the time interval, wherein the longitudinal coordinates of the optical waveguide can be associated with corresponding temperature values.
For localizing leakages particularly in ascending or supply pipes of underground gas accumulators, so-called flow meter measurements have become known, wherein the gas flow from the surrounding annular space into the actual bore hole is detected. Back-pipe effects cannot be determined by means of flow measurements, as such effects do not entail a gas flow within the piping. The local resolution of known flow meter measurements is determined by the respective discrete depths in which the measurement is carried out and is, therefore, basically small.
Moreover, it has already been suggested to seal the annular spaces one after the other in selected deep areas in order to perform pressure measurements. In this case, however, merely the incoming gas flowing into the actual piping is determined, and the local resolution is small in dependence on the sealing steps. Furthermore, the costs for such pressure measurements are considerable.
For testing the tightness of the base sole and lateral walls of or in building excavations, respectively, individual bores are provided in the excavation in order to detect in one after the other the temperature by means of a lance, the tip of which is provided with a temperature sensor. In other words, the temperature is determined at the bases of the individual bores by means of the lance and the temperature sensor provided thereon. The detection of a temperature development in terms of time is not possible or only with problems. The surface-related temperature plot produced at the end of the measurements performed in the known manner is hard to interpret as the temperature values were not determined at the same time. The water has to be pumped out of the building excavation until the measurement of all bores is completed. Given a large building excavation this results in high pumping times, wherein the disadvantage of the cited known solution moreover consists in that monitoring of the vertical wall is not possible or only realizable with restricted quality.
As was mentioned above, the fiber-optic temperature sensing mechanism is excellently suited for monitoring pipelines such as product pipelines, distant heating pipes etc. and in this respect particularly for the detection of leakages. The development of the temperature in terms of time or the temperature itself contains information on the current operating state of the monitored pipeline. Leakages result in local temperature anomalies, which develop within a short time, i.e. within a few minutes up to hours. Said anomalies are detected and located by means of the described measuring method relating to fiber-optic temperature sensing. Temperature deviations depending on the time of day and year or on the weather are at all times spacious appearances with a relatively long-time constant. In contrast to other temperature deviations the leakages can be detected and located by the spacial limitation and their development in terms of time. The response time of the used leakage detection systems depends on a plurality of technical parameters such as the leakage rate, the kind of product, the pressure, temperature, the quality of the ground, the local and temperature resolution of the fiber-optic temperature measuring technology and others. The response time of the leakage detection system required for respective use determines the time interval xcfx84 with which the temperature profiles have to be determined. As large quantities of data have to be processed by taking into account reference values in each case, and as it is necessary to constantly remove natural temperature variations from the current measuring values, known evaluation methods require a lot of time and/or calculations, so that an online evaluation is partially not possible or only with restrictions.
According to the above it is the object of the invention to provide a method for monitoring, also permanently and automatically, temperature distributions and/or temperature anomalies on the basis of distributed fiber-optic temperature sensing, which permits to improve the evaluation of the measured values and to simultaneously increase the accuracy of the information provided by the measurements. Moreover, the method to be provided is to be suited for long-time tests and is to securely detect local extremes without requiring laborious numeric derivations.
Another object of the invention resides in providing a device for monitoring temperature distributions and/or temperature anomalies, in particular of ascending or supply pipes for underground gas accumulators surrounded by an annular space, by means of fiber-optic sensor cables for determining the temperature distribution, which results in an inexpensive high local resolution of the respective measurements or leakage detections and which excludes the safety risks in the continued or uninterrupted storage operation.
Another object of the invention resides in the provision of a method for monitoring on the basis of distributed fiber-optic temperature sensing, in particular for proving the tightness of base sole and lateral walls in building excavations or similar facilities, wherein pumping times are to be cut shorter and wherein by means of a virtually simultaneous measurement information on defects in the base sole and the wall elements of the excavation are obtained in a highly precise and fast manner.
Another object of the invention resides in detecting underground water flows and/or the position of a watershed by means of fiber-optic temperature sensing, without having to work with means or so-called tracers which are hazardous to the environment.
Finally, it is an object of the invention to open up new application fields in connection with fiber-optic temperature sensing, whereby especially chemical or micro-biological leaching processes or methods are to be taken into account.
The solution to the object of the invention in view of the long-time monitoring is provided with a method comprising the steps of:
determining a sum of naturally existing temperature variations during the normal operation of a corresponding measuring device and deriving reference profiles thereof;
generating a matrix Aij having a size defined by the number of the longitudinal sections of the sensor cable I=L/xcex94x and the number J of the reference profiles;
executing individual profile measurements at short time intervals and forming a mean value profiles thereof;
deriving the current profile Ti,t,n,w,n from the mean value profile and storing said profile in a table;
evaluating the current stored profiled stepwise for all j-values, i.e. by comparison with the different reference values TRef,i,j, wherein the resulting temperature differences xcex94T(Xi) for all longitudinal sections i are checked for a deviation larger than a threshold value ∂ (noise);
determining whether the deviations exist for one or more i-values, and checking wether the deviations exist in a plurality of adjacent longitudinal sections, wherein in case of existence of comparable temperature deviations from the reference values of the profile large-surface temperature changes are concluded in the positive case and a leakage is concluded in the negative case. Reference is made to the individual claims and the description as far as partial objects to be solved are concerned.
With the method according to the invention for monitoring, also permanently and automatically, temperature distributions and/or temperature anomalies, at first a determination of a quantity of naturally existing temperature variations during the normal operation and the derivation of so-called reference profiles based thereon is assumed.
In the following, a matrix Aij having a size defined by the number of the longitudinal sections of the sensor cable and the number of reference profiles is generated.
Within short time intervals individual profile measurements are then performed, whereof a mean value profile is determined. A current profile is then determined from the mean value profile, and said current profile is stored, preferably in a table.
Additionally the current, stored profile(s) is/are then evaluated step by step in view of all individual values by comparing them with the different reference profiles, whereby the temperature differences resulting for all longitudinal sections are then examined for a deviation larger than a threshold value.
Thereafter it is determined, whether the deviations exist for one or more values, and it is examined whether the deviations have occurred for a plurality of adjacent longitudinal sections. If comparable temperature deviations from the reference values of the profile exist, spacious temperature changes are concluded in the positive case, and a leakage in the negative case.
Accordingly, the current temperature profile T(xi,t) is compared with different reference profiles and evaluated by means of criteria to be defined. In this respect xi designates the longitudinal coordinate of the individual measuring intervals [xixe2x88x92xcex94x/2, xi+xcex94x/2] of the sensor cable, wherein xcex94x is the local resolution of the measuring system.
The essential values to be modified in view of the respective monitoring task relate to the threshold value ∂ for the temperature difference xcex94T(xi)=T(xi,t)xe2x88x92TRef(xi) and the time interval xcfx84 between the measurements of the temperature profiles.
The temperature profiles measured at time t-xcfx84 as well as reference data with corresponding static information contents serve as reference profiles TRef.
Said reference data are permanently updated and statistically evaluated during the operation of the respective system. They contain local information on the temperature deviations in view of daytime and season as well as climatic influences. The permanent updating and the expansion of the catalogue of the reference profiles make the system self-learning, and it independently adjusts to the individual situations.
In view of the time dynamics of the measurements it must be noted that the used fiber-optic sensor cable results in a short delay of the temperature measurement due to its construction, which can last up to several minutes in dependence on the thermal contact with the ambient medium. The leakage itself normally develops very fast at first, in order to slowly change into a quasi stationary state thereafter. According to the invention said property is used for the selection of the time intervals between the individual measurements of the temperature profiles, in order to optimize the calculation work and to shorten the time for evaluation.
According to the invention natural temperature variations are constantly removed from the updated measured values by means of correction so that temperature anomalies deriving from the actual leakages clearly stand out in the temperature difference profiles (xcex94T (xi). This takes place by the comparison with the measured values, which were measured shortly before or also some time ago. If there are no precise results it is additionally possible to use so-called historic data lying further back, which were determined successively in the course of longer measurements.
In view of the processing of historic data the calendar year is preferably divided into 52 annual weeks in order to be able to refer to precise reference data, which account for the seasonal temperature variations. The remaining day, two in leap years, is, for instance, added to the last calendar week of the year. At time intervals xcfx84, for example, xcfx84=1 h, the current temperature profiles Ti,t,n,w,N are then continuously measured and stored. The indices thereby refer to:
i=longitudinal section
t=time
n=week day
w=running number of the calendar week
N=current year since the monitoring system started to operate.
The stored values serve the comparison of the current temperature profile with the previous temperature profiles in order to form difference values xcex94T(xi)=Ti,t,n,w,Nxe2x88x92TRef,j thereof.
If local, i.e. for a few adjacent xi temperature differences occur, which are larger than the predefined response threshold ∂, said temperature anomaly indicates a leakage.
The mean temperature measuring values being representative for each week of the year as well as supplementary some selected statistic values are transferred into a data base according to the invention, the data field of which results from the reference time or daytime, respectively, and to the individual calendar weeks.
Each data field then contains the following stored values:
1. the running number of the current year N (N=1,2,3 . . . ) since the monitoring system started to operate;
2. the updated mean value  less than Ti,r,w greater than N of the weekly mean value of the temperature  less than Ti,r,w,N greater than  for all longitudinal coordinates xi and for all reference times r=tRef                                          ⟨                          T                              i                ,                r                ,                w                ,                N                                      ⟩                    =                                                    ⟨                                  T                                      i                    ,                    r                    ,                    w                    ,                    N                                                  ⟩                            +                                                (                                      N                    -                    1                                    )                                ·                                                      ⟨                                          T                                              i                        ,                        r                        ,                        w                                                              ⟩                                                        N                    -                    1                                                                        N                          ⁢                  
                ⁢                                                            mit                ⁢                                  ⟨                                      T                                          i                      ,                      r                      ,                      w                      ,                      N                                                        ⟩                                            =                                                1                  7                                ⁢                                                      ∑                                          n                      =                      1                                        7                                    ⁢                                      xe2x80x83                                    ⁢                                      T                                          i                      ,                      r                      ,                      n                      ,                      w                      ,                      N                                                                                            ;                          xe2x80x83                        ⁢                          w              =              1                                ,          …          ⁢                      xe2x80x83                    ,          52                                    (        1        )            
wherein  less than Ti,r,w,N greater than  is in each case calculated upon the expiration of the last calendar week w;
3. the updated mean value  less than "sgr"2i,r,w, greater than N of the square deviation of the weekly temperature mean value from the updated temperature mean value  less than "sgr"2i,r,w,N greater than  for all longitudinal coordinates xi and all reference times r=tRef                                          ⟨                          σ                              i                ,                r                ,                w                ,                            2                        ⟩                    N                =                                                            ⟨                                  σ                                      i                    ,                    r                    ,                    w                    ,                    N                                    2                                ⟩                            +                                                (                                      N                    -                    1                                    )                                ·                                                      ⟨                                          σ                                              i                        ,                        r                        ,                        w                                            2                                        ⟩                                                        N                    -                    1                                                                        N                    .                                    (        2        )            
with  less than "sgr"2i,r,w,N greater than =( less than Ti,r,w,N greater than xe2x88x92 less than Ti,r,w, greater than N)2.
The values shown in equations (1) and (2) accordingly contain information on the naturally existing temperature variations during the normal operation of, for instance, a pipeline and can be used for evaluating currently measured temperature fluctuations. The date themselves can be updated step by step in the course of the year or within other pre-definable time segments.
In a supplementary step it is possible to check by means of the preceding sign of the detected anomaly whether the expected physical effect has been provided, in order to then correct or respectively expand the matrix elements for the ongoing performance of the method.
In view of the monitoring of ascending or supply pipes surrounded by an annular space for underground gas accumulators by means of fiber-optic sensor cables, said sensor cable is arranged inside the ascending or supply pipe and/or a high-pressure gas pipeline for determining the temperature distribution or for detecting anomalies. The sensor cable is passed towards the outside via a pressure-proof sealing. Moreover, a device or means are provided for the temporary relief of the pressurized annular space and/or the ascending pipe in order to relieve either the pressurized annular space or the ascending pipe space itself once the initial state of the temperature distribution has been determined. Said pressure relief takes place only for a short time so that the storage operation is not considerably interrupted.
A measuring unit for feeding radiation impulses and for receiving Raman backscatter radiation is connected to the exterior end of the here used fiber-optic sensor cable.
According to a preferred embodiment a weighted body is fastened to the interior end of the sensor cable to be lowered into the pipe, allowing the cable to be arranged in the pipe in a freely suspended manner. Also the arrangement of a cable end box or terminal box is possible, such as is described in DE 43 04 546 C1.
In the case, where a defined position of the sensor cable in the interior of the pipe is desired due to measurement-technical or other reasons, springy spacers are attached to the sensor cable section by section, which upon inserting the sensor cable inside the pipe secure a position thereof that is predefined or can be predefined.
The springiness of the spacers makes sure that the sensor cable can also be inserted via a pressed air lock having only a small diameter. In the relaxed state the springy spacers have a position essentially vertical to the longitudinal axis of the sensor cable or extend from said axis to the inside wall of the ascending or supply pipe in a vertical direction.
The temperature anomalies detected by the device in measured temperature profiles supply information on leakages in the piping or on flow processes in the rear area of the pipe, i.e. in the so-called annular space. As is shown by the device, this is surprisingly also possible if the sensor cable is installed in the supply pipe. Coolings, i.e. temperature changes in the annular space or the cementation have a backwards effect into the supply pipe via heat conduction processes and can be measured by means of the fiber-optic temperature sensing mechanism, evaluated with the aforementioned method and located.
In view of the evaluation, a differential curve of the temperature profiles is determined prior to and after the relaxation of the annular space to be effected, wherein said curve shows anomalies with differed preceding signs. Negative temperature differences imply leaky pipe bells, whereas positive temperature differences and anomalies show the incoming flow of warmer gas in the rear area of the pipe due to a damaged cementation or sheathing.
Therefore, the described device enables a simultaneous, distributed measurement of the temperature depth profiles alongside of the total accumulator bore in natural gas accumulators with high local and temperature resolution given a large sensor cable length. The detectable temperature range lies inbetween xe2x88x9250xc2x0 C. up to more than 350xc2x0 C. at pressures of up to 75 MPa.
An influence of the storage operation through the inventive device is excluded. Due to the fact that the sensor cable has no potential- or current-carrying wires whatsoever, there is no explosion hazard right from the beginning. The used fiber-optic sensor cables of the device are mechanically and chemically extremely resistant and have a long lifetime. The fiber-optic sensor cables may remain in the interior of the pipe permanently and enable critical date measurements and permanent monitoring by connection to electronic data processing control rooms.
Alternatively a temporary installation of the sensor cable into the bore of a gas accumulator is possible, whereby the sensor cable is inserted into the pressurized bore by means of pressed air locks for sealing the bore during the installation of the cable and during the actual measurements. Here, too, the pressurized annular space or the ascending pipe is relieved upon the determination of an initial temperature state, and a new temperature detection takes place. Measurements can be made in aquifer storages as well as in a cavern or in exploited deposits for the storage of gas.
It has shown that a local allocation of leakages up to an accuracy of 0.25 m can be achieved with the proposed device, so that an exact determination of defect or leaky parts can be performed by means of a given piping scheme. By means of an additional sensing mechanism in the able terminal box or cable end box further physical parameters can be detected. By arranging a geophone in or on the box, the gas/water contact during the insertion of the sensor cable can be determined in an advantageous manner, and an undesired swinging of the loom of cables with possibly resulting damages due to abruptly changed pressure conditions can effectively be prevented.
When laying the sensor cable in the interior of a high-pressure gas pipeline, which, for example, leads through a densely populated area where earth works are not possible or only with problems, a composite cable having a plurality of optical waveguides is used in order to obtain a data transmission, particularly for telecommunication purposes, in addition to the leakage detection.
With the inventive method for proving the tightness of base sole and lateral walls in building excavations or the like installations on the basis of distributed fiber-optic temperature sensing, at first a grid-like executed number of bores is inserted down to the base sole in correspondence with the geometry of the excavation. Temperature probes are then inserted into said bores and the probe measuring results are read out.
If an anomaly is detected it is possible to switch the measurement from a coarse grid to a fine grid in order to be able to locate the leakage more exactly.
Furthermore, bores are inserted in the direct proximity of sheet pilings and subterraneous curtains in front of the joints of the individual wall elements, whereby said bores reach down to the base sole.
A continuous fiber-optic cable is then introduced into said additional bores, whereby basic weights or weighted bodies are used for said purpose.
After the initial state of the temperature distribution has been determined the water is pumped out of the interior of the excavation and the adjusting temperature distribution is measured in a continuous or cyclic manner. By means of continuous or cyclic comparison with the initial state, leakages can then be concluded online, whereby here, too, the positions of the individual leaky spots can be determined.
According to the invention, the above described method takes into account the existing temperature differences between the water flowing in through a possible leakage and the ambience of the sealing system. In the concrete case of a building excavation base sole heat is generated during the cementation process. Accordingly the temperature in the building excavation can rise to values of more than 20xc2x0 C. above the base soil sealing. This results in clear temperature differences between the ground water outside the excavation and the water inside the excavation. When pumping the water out of the interior of the building excavation the ground water level is reduced in the sealed building excavation and a hydraulic gradient as well as an additional hydrostatic pressure are created. Said hydraulic gradient has the effect that through a leakage in the base sole, in the vertical walls, i.e. on sheet pilings or subterraneous curtains, and in the area of the base sole/wall connection clearly cooler ground water having a temperature for example of 10 to 13xc2x0 C. penetrates into the building excavation. By measuring the temperature distribution on the base sole of the building excavation and on the vertical walls, as was described above, during the pumping, leakages can easily and securely be detected in the corresponding sealing installations or systems.
In the further inventive method for monitoring temperature distributions and/or temperature anomalies, in particular for determining flows in excavation waters as well as for determining the behavior of a watershed, again fiber-optic sensor cables are used.
The fiber-optic cable(s) is/are inserted, preferably meander-like, in the drift or in the excavation laterally or extending in a longitudinal direction, however, by covering surface elements as large as possible.
Moreover, a thermal point source is activated preferably in the center of the cable arrangement, whereby on the basis of a detected displacement of the determined temperature profiles relative to the known position of the point source the existence of a flow on one hand but also the flow rate on the other hand can be concluded.
According to the invention the direction of flow of the excavation water can so be determined and the flow rate can be estimated in a flooded drift section being completely filled with water. This takes place with a combination of a thermal point source, e.g. local heating or cooling, and a distributed temperature measurement, i.e. simultaneous measurements of temperature and location. The point source works as a thermal impulse only with a time limit.
It has shown that despite the existing heat conduction in the water, small flow rates can be determined by shifting the determined temperature curve.
The measuring method makes it possible to waive otherwise required tracers, which would entail environmental impacts. By activating the thermal point source anew, the measurement with a once installed fiber-optic cable can be repeated and updated at any time, whereby the monitoring of critical ground water or base sole sections with the purpose of monitoring for example flooded mine installations is possible.
A novel application of the method according to the invention for determining temperature distributions and/or temperature anomalies on the basis of distributed fiber-optic temperature sensing consists in the evaluation of chemical or microbiological leaching processes. In this respect the knowledge is used that the leaching activities take place exothermally and that a control of the leaching process by means of an evaluation of the march of the temperature in a leaching dump or leaching fill becomes possible.
According to the invention meander-shaped fiber-optic sensors are preferably inserted when building the leaching dump or leaching fill, whereby the respective meanders cover the dump or fill surface in a grid-like manner. At least two surface structures more or less forming levels are arranged in the dump or fill on top of each other.
The spacial distribution or the configuration of the meander can take place in the grid of 1, 0.5 or 0.25 m.
By means of a common measuring device the temperature distribution may then be determined both within a level in a planar manner and of the levels arranged on top of each other against one another.
It is according to the invention that, of course, also a spiral-shaped or other planar laying of the sensor cable rather than a meander-like one is conceivable.
With the aid of the inserted fiber-optic sensing mechanism both the local and the temporal structure of the leaching front within the dump or fill can be determined, and it is possible to check whether the leaching is homogeneous. In the case of inhomogeneities fresh substance can purposively be added.
By the arrangement of at least two or more levels of sensors arranged in a planar manner, preferably horizontally one above the other, flows within the fill or dump can be detected and evaluated and used for the evaluation or control of the leaching process.
By means of the simple temporal detection of forming water fronts also the relaxing time after exothermal reactions can be monitored and a new process start can be initiated or also the state of the exhaustion in view of the leaching process can objectively be determined.
As can be inferred from the aforementioned explanations, the evaluation method allows to improve the accuracy especially during long-time monitoring on the basis of determining temperature distributions by means of fiber-optic sensing, wherein, by considering a reference data base, an online evaluation can take place with a small extent of calculations.
By means of said improved evaluation method new cases of application for the distributed temperature measurement can be opened up by means of fiber optics, whereby especially the detection of leakages in ascending or supply pipes in gas accumulators, and also the determination of tightness of the base sole and the lateral walls in building excavations is pointed out in this respect.
It has, moreover, shown that it is possible on the basis of the evaluation accuracy to determine underground flows also with very small flow rates, e.g. in flooded open drift sections. An additional novel case of application resides in the evaluation of exothermal reactions of chemical and/or microbiological leaching processes, so that such methods can be monitored and controlled in situ, with the result that an increased exploitation is achieved with a simultaneous more effective operation of such plants and installations.